Ice dam leaks in Manchester

How an ice dam forms

Warm air from the house leaks into the attic and warms the roof deck. Snow melts on the upper roof, runs down to the eaves, which stay cold, and freezes again. The ridge grows, and the next melt has nowhere to go but under the shingles. Extension services at Missouri, North Dakota State and Michigan State all describe the same cause: uneven roof temperatures driven by heat loss from the living space.

How often the setup happens here

We counted days in Concord's long weather record when at least 6 inches of snow sat on the ground, the high reached 36°F or more, and the low that night or the next fell to 28°F or below. That melt and refreeze is what builds a dam. An average winter had 21.3 such days over the winters of 1991-92 to 2020-21 and 22.6 over the winters of 2015-16 to 2024-25, most of them in February (9.6 on average). Snowfall dropped from 67.6 to 56.5 inches a season over the same span; the thaw days didn't.

Ice dam weather: thaw-and-refreeze days with 6+ inches of snow on the ground, per winter

Inside the house

Ice dam water usually shows up as a stain at the top of an exterior wall, water around a window head, or drips from a ceiling light near the eaves. By then the insulation above is often soaked. A restoration company checks the ceiling and wall cavities with a moisture meter, removes wet insulation and drywall, and dries the framing. Wet insulation left in place holds water against the wood, and the extension services warn that ice dam water can decay framing and grow mold in attics and walls.

On the roof

• A roof rake from the ground, pulling the first few feet of snow off the eaves, is the safe homeowner step.
• Steam removal is the professional method; Fixr lists it at $400 to $600 per hour. Chipping with a hammer or an axe damages shingles.
• Heat cable treats the symptom. NDSU's extension cautions that homeowners often reach for heat tape instead of preventing the cause.

Fixing the cause

Seal the air leaks between the house and the attic first (around plumbing and wiring holes, recessed lights and the attic hatch), then add insulation, with ventilation working alongside. Missouri Extension suggests R-38 for ceilings and roofs. That work is cheaper than a ceiling repair every February.